The ability of crystalline alkali metal aluminosilicate (zeolite) to sequester calcium ions from aqueous solution has led to its becoming a well-known replacement for phosphates as a detergency builder. Particulate detergent compositions containing zeolite are widely disclosed in the art, for example, in GB 1 473 201 (Henkel), and are sold commercially in many parts of Europe, Japan and the United States of America.
Although many crystal forms of zeolite are known, the preferred zeolite for detergents use has always been zeolite A: other zeolites such as X or P(B) have not found favour because their calcium ion uptake is either inadequate or too slow. Zeolite A has the advantage of being a "maximum aluminium" structure containing the maximum possible proportion of aluminium to silicon--or the theoretical minimum Si:Al ratio of 1.0--so that its capacity for taking up calcium ions from aqueous solution is intrinsically greater than those of zeolite X and P which generally contain a lower proportion of aluminium (or a higher Si:Al ratio).
EP 384 070A (Unilever) describes and claims a novel zeolite P (maximum aluminium zeolite P, or zeolite MAP) having an especially low silicon to aluminium ratio, not greater than 1.33 and preferably not greater than 1.15. This material is demonstrated to be a more efficient detergency builder than conventional zeolite 4A.
EP 448 297A and EP 502 675A (Unilever) disclose detergent formulations containing zeolite MAP with a cobuilder (citrate or polymer), and also containing sodium perborate monohydrate bleach and TAED bleach precursor. Compositions containing zeolite MAP exhibit better detergency than corresponding compositions containing zeolite 4A.
It has now been discovered that replacement of zeolite A by zeolite MAP gives an additional benefit in detergent powders of high bulk density (700 g/1 and above) containing sodium perborate monohydrate bleach: the stability of the sodium perburate monohydrate on storage is significantly increased. This is surprising because the water content of zeolite MAP is not significantly lower than that of zeolite A.